Guns are often equipped with a front sight and a rear sight to provide a two-point visual reference for locating an intended target.
A user views the target through the rear sight, closest to the user's eye, and then aligns the front sight, typically a pin, on the target.
The rear sight is sometimes equipped as a “peep sight,” or a circular structure with a void space in the middle for referencing and framing the front site. With the increasing use and popularity of long-range firearms such as rifles, the use and popularity of scope sights have likewise increased.